In my opinion hes even more than 40 mio worth compared that we bought Paulinho for 40 mio. Seri is younger, played last season in a better league and had a pretty good season
Before this crazy summer i would have said 25-30 mio would be okay for him
If he is worth more than he costs you would expect to see more teams interested in him, but there aren't. 40m is a small sum in this market and there are many clubs ready to pay such sum to get a Barca quality midfielder, but he isn't a Barca quality player.
He had a season like the one Mahrez had when Leicester won the league. He is nothing special and isn't anywhere near the quality player we are looking for to improve the midfield.
The board did enough mistakes in buying relatively cheap players in their attempt to improve the team and they are now struggling to sell them.
If you add what the club paid for Arda, Gomes and Paulinho, you can get a top quality player who can improve the team. But instead we have 3 useless players with high wages and low market value.